Although the cardiac muscle syncytium has been extensively studied over the past three or four decades the understanding of the way in which the cell membrane produces action potentials, and the mechanism by which these action potentials travel across cell boundaries is still very incomplete. It seems clear that the major obstacle has been the small size of cardiac cells and the complicated geometrical arrangement in which they are assembled. To improve knowledge on these areas we propose to use experimental preparations which have properties of propagation analogous to cardiac muscle but lack the geometrical complexity of true syncytial tissues. These preparations are nerve axons, in particular squid and crayfish axons where functional properties similar to those of cardiac muscle can be found or produced by drugs. The objectives of the present series of studies are: 1) To determine the usefulness of squid axons perfused with tetraethylammonium (TEA) as a model system to generate membrane action potentials with characteristics similar to those of cardiac muscle. 2) To examine an axon preparation useful to study propagation of cardiac-like action potentials in single cells. 3) To develop an axon preparation of two electrically coupled axons, to study propagation of cardiac-like action potentials across cell boundaries via electrotonic synapses.